1. Field of the Invention
The present invention relates to a piezoelectric element feeder and a method of measuring electric characteristics of a piezoelectric element, the piezoelectric element feeder and the method used when manufacturing, for example, a head suspension being a device installed in a hard disk drive of an information processing apparatus such as a personal computer.
2. Description of Related Art
Recent hard disk drives are required to have very large capacity. To realize this, the number of tracks per inch (TPI) on a hard disk in the hard disk drive becomes more and more increased to narrow the width of each track. To access such narrow tracks, there is a need for an actuator that is capable of precisely positioning a head of a head suspension within a minute range across the tracks.
To meet the need, the applicant of the present invention has proposed in Japanese Unexamined Patent Application Publication No. 2010-86649 a head suspension employing a dual actuator system. The dual actuator system uses a piezoelectric element in addition to a usual voice coil motor that drives a carriage to which the head suspension is attached. The piezoelectric element is arranged between a base plate and load beam of the head suspension, to finely move the head attached to the load beam relative to the base plate.
FIG. 9A is a plan view roughly illustrating a head suspension 101 according to a related art (Japanese Unexamined Patent Application Publication No. 2012-11378). FIG. 9B is an equivalent circuit of piezoelectric elements installed in the head suspension 101 of FIG. 9A, and FIG. 9C illustrates deformation of the piezoelectric elements.
The head suspension 101 has a base plate 103, a load beam 105, and the pair of piezoelectric elements 107a and 107b. The piezoelectric elements 107a and 107b are arranged between the base plate 103 and the load beam 105, are oppositely oriented, and are arranged in parallel with each other to form an actuator 109. A front end of the load beam 105 supports a read/write head 111 that is movable with the load beam 105 relative to the base plate 103.
The piezoelectric elements 107a and 107b oppositely deform according to a voltage applied thereto. Namely, one of the piezoelectric elements 107a and 107b expands and the other contracts, to slightly move the head 111 with the load beam 105 relative to the base plate 103 in a sway direction, i.e., a width direction of the head suspension 101 in which the piezoelectric elements 107a and 107b are arranged side by side.
For this structure and operation, the piezoelectric elements 107a and 107b must be attached to the head suspension 101 as correctly as designed.
The pair of piezoelectric elements 107a and 107b have the same appearance, and therefore, are hardly distinguishable from each other or between the back and front of each. Due to this, there is a risk of shipping the head suspension 101 with the piezoelectric elements 107a and 107b incorrectly installed.
To avoid such trouble, there is an idea of imprinting marks on the piezoelectric elements 107a and 107b to distinguish them from each other or between the back and the front. This technique, however, produces contaminants, and therefore, is impracticable.
There is another idea to apply voltage to the actuator 109 measure an actual stroke of the head 111, and determine if the piezoelectric elements 107a and 107b are correctly installed. The actual stroke of the head 111 is in the range of 50 to 100 nanometers, and therefore, this technique needs precision measuring equipment that is expensive.
U.S. Pat. No. 6,639,411 teaches a method of detecting whether or not piezoelectric elements of a head suspension are correctly oriented or have any defects according to signals that are obtained by forcibly displacing the head suspension.
FIG. 10A illustrates the head suspension 101 of FIG. 9A installed in a hard disk drive and FIG. 10B illustrates the head suspension 101 in a free state. As is apparent from comparison between FIGS. 10A and 10B, load on the load beam 105 of the head suspension 101 differs between the installed state of FIG. 10A and the free state of FIG. 10B. If, in the free state of FIG. 10B, a voltage is applied to test the piezoelectric elements 107a and 107b, only unstable data will be provided because the movement of the load beam 105 is unstable or variable in the free state of FIG. 10B. With such unstable data, the technique of the U.S. Pat. No. 6,639,411 is unable to determine whether or not the piezoelectric elements 107a and 107b are correctly installed.
There is another problem that a circuit breakage of the actuator 109, if any, is hardly detectable.
To solve these problems, the applicant of the present invention has proposed in the Japanese Unexamined Patent Application Publication No. 2012-113782 a method of testing piezoelectric elements according to C-V characteristics thereof. This method tests a finished head suspension into which a piezoelectric element is installed, and therefore, involves a problem that, if the piezoelectric element is tested as defective, the head suspension as a whole is accordingly defective by necessity.
Accordingly, there is a need for testing a piezoelectric element before its installation in a head suspension, to reduce defective head suspensions.